During the coking of coal, waters are produced which contain not only organic and non-volatile anorganic matter, but also volatile inorganic matter such as ammonia, hydrogen sulphide and prussic acid. These volatile inorganic compounds need to be removed to the maximum possible extent before these waters are recycled to the process for washing and scrubbing purposes, or--in the majority of cases after further treatment for removal or partial removal of other noxious matter--are discharged into the sewage. The removal of volatile inorganic matter contained in such waters is normally carried out in the coke-oven plant in stripper columns by means of steam. Aside from steam, other gases can be used as stripping gases.
German patent document DE-OS No. 14 44 972 contains a proposal to subject water from the gas collecting main of a coke-oven plant to a stripping process with an inert gas such as air, flue gas, or a blend of both for removing ammonia and phenols.
Because of the unsatisfactory proceeds from ammonia sales more and more ammonia destruction units are operated in coke-oven plants (E. TH. Herpers; Haus der Technik, lecture, Vortragsveroffentlichung 470, p. 41 to 50). These cracking units are run on vapors from stripping columns which contain mainly ammonia, carbon dioxide, and steam; generally also present prussic acid and hydrogen sulphide. While prussic acid is cracked completely, and ammonia as well, except for a small remainder, the hydrogen sulphide remains unaffected. Accordingly, the cracked gases need to be cleaned. This is normally done by cycling cracked gases after waste-heat recovery and cooling to the raw-gas cleaning process. After waste-heat recovery (steam production), the cracking gas still contains energy which, however, is qualified as of low value, and therefore is discharged (Gas- und Wasserfach, Heft 9 (1964), p. 225 to 232).